All electrical installations and equipment comply with insulation resistance specifications so they can operate safely. Whether it involves the connection cables, the sectioning and protection equipment, or the motors and generators, the electrical conductors are insulated using materials with high electrical resistance in order to limit, as much as possible, the flow of current outside the conductors. Insulation resistance measurement is nondestructive under normal test conditions.
Carried out by applying a DC voltage with smaller amplitude than for dielectric testing, it yields a result expressed in kW, MW, GW or TW. This resistance indicates the quality of the insulation between two conductors. Because it is non-destructive, it is particularly useful for monitoring insulation aging during the operating life of electrical equipment or installations. This measurement is performed using an insulation tester, also called a megohmmeter.